I. Field of the Disclosure
The technology of the disclosure relates generally to charging a battery of portable electronic devices over a Universal Serial Bus (USB) cable connected to a USB host.
II. Background
Portable electronic devices, such as smartphones, tablets, laptop computers, and the like, can be powered by rechargeable batteries. These rechargeable batteries require periodic recharging. Universal Serial Bus (USB) is an industry standard that defines cables, connectors, and communications protocols for data and power transfers among personal computers and electronic devices. Ports can be used for both data transfer ports as well as charging ports to charge rechargeable batteries of portable electronic devices.
In this regard, FIG. 1 illustrates a physical connectivity between a USB Specification Revision 2.0 (USB 2.0) controller 10 in a USB 2.0 portable electronic device 12 (“portable device 12”) and a USB 3.x controller 14 in a USB 3.x host 16. The USB 2.0 controller 10 and the USB 3.x controller 14 are controlled by a USB 2.0 software driver 11 and a USB 3.x software driver 15, respectively. On one end, the USB 2.0 portable device 12 is embedded with a USB 2.0 micro-B receptacle 18. On the other end, the USB 3.x host 16 exposes a USB 3.x enhanced SuperSpeed standard-A receptacle 20. A detachable USB 2.0 cable 22, with a USB 2.0 micro-B plug 24 on one end and a USB 2.0 standard-A plug 26 on the other end, connects the USB 2.0 portable device 12 to the USB 3.x host 16. The USB 2.0 cable has a VBUS conductor, a GND conductor, a D− conductor, and a D+ conductor. The USB 2.0 micro-B receptacle 18 has a VBUS pin 28(1), a GND pin 30(1), a D− pin 32(1), and a D+ pin 34(1). The VBUS pin 28(1) and the GND pin 30(1) are used for charging, while the D− pin 32(1) and the D+ pin 34(1) are used for protocol handshakes and data transfer. The USB 3.x enhanced SuperSpeed standard-A receptacle 20 has a USB 2.0 interface 36 and a USB 3.x SuperSpeed interface 38. The USB 2.0 interface 36 has a VBUS pin 28(2), a GND pin 30(2), a D− pin 32(2), and a D+ pin 34(2). The USB 3.x SuperSpeed interface 38 has additional pins, namely a SSTX− pin 40, a SSTX+ pin 42, a SSRX− pin 46, and a SSRX+ pin 48. The SSTX− pin 40 and the SSTX+ pin 42 are used for SuperSpeed transmissions, while the SSRX− pin 46 and the SSRX+ pin 48 are used for SuperSpeed receptions.
The USB 2.0 portable device 12 in FIG. 1 is allowed to draw up to 500 mA charging current from the USB 3.x host 16 as a connected standard downstream port (SDP) according to Battery Charging Specification 1.2 (BC1.2). By means of hardware-based mechanism specified in USB 2.0, the USB 2.0 controller 10 presents itself as a USB 2.0 compatible device by pulling the D+ pin 34(1) HIGH. The USB 3.x controller 14 then detects the USB 2.0 portable device 12 as a USB 2.0 compatible device and selects the operating mode of the USB 2.0 portable device 12 according to USB 2.0. USB 2.0 provides for standard message descriptors to be exchanged between USB devices and hosts for charging purposes. Thus, the USB 3.x controller 14 will allow the USB 2.0 portable device 12 to draw up to 500 mA according to BC1.2 even though the USB 2.0 cable 22 is capable of safely carrying more current. However, if the USB 2.0 portable device 12 was instead a USB 3.x compatible device connected to the USB 3.x host 16 with a USB 3.x cable (not shown), the USB 3.x controller 14 would allow the USB 2.0 portable device 12 to draw up to 900 mA for faster charging time according to BC1.2.